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(No Model.) 3 Sheets-Sheet 1.

P.RABBIDGE. TELEPHONE.

No. 488,367. Patented Dec. 2o, 1892.,

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3 Sheets-Sheet 2.

(No Model.)

P. RABBIDGE.

TELEPHONE.

No. 488,867. Patented Dec'. 20, 1892.

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(No Model.) 3 Sheets-Sheet B.

P. RABBIDGB. TELEPHONE.

No. 488,887. Patented Deo. 2o, 1898.

PARNELL RABBIDGE, OF SYDNEY, NEW SOUTH VALES.

TELEPHONE..

SPECIFICATION forming part of Letters Patent No. 488,367, dated DecemberV 20, 1892.

Application filed March 3, 1892. Serial No. 423,670. (No model.)

To all whom it may concern:

Be it known that I, PARNELL RABBIDGE, a subject of the Queen of Great Britain and Ireland, anda resident of Sydney, in the Colony of New South lVales, Australia, have invented Improvements in Telephones, of which the following is a specification.

This invention relates more particularly to that class of telephone that is used for speaking through short distances, and is especially applicable to use in large buildings.

The apparatus comprises a base-plate to which is attached an insulating base-plate to which is secured a call bell that covers the operating electro magnet. Superimposed upon the bell, and insulated from it, is the transmitter` which includes a microphono. Secured to the metal base plate is a flexible tube, preferably composed of a helix of wire, and to the extreme end of which is attached the receiver. Contained within the flexible tube, and preferably at the receiver end, is a gravity switch of any approved design; the object of the gravity switch being to switch in and out the bell and the transmitter circuits as the receiver is raised to or lowered from the ear of the operator.

In the accompanying drawings Figure l is a front view of the apparatus .as it appears when in position on the wall. Fig. 2 is a cross section of the same. Fig. 3 is a front view of the apparatus as it would appear when in position on the wall, but with the transmitter and the gong removed, for the purpose of showing the arrangement of the bell magnet. The flexible tube and the receiver are also removed as they are not required in reference to this figure. Fig. 4 is a detail plan view of part of the transmitter showing the microphone. Fig. 5 is a detail showing the tube and the transmitter in vertical section, and the gravity switch in place. Fig. 6 is a detail longitudinal section showing the form of gravity switch that is preferably used. Fig. 7

shows a modification in arrangement of telephones especially adapted for use at an office desk. Fig. S is a diagram showing' the circuits when the transmitter is at rest and also when it is being used.

A, is the metal base plate, by which the telephone is secured to the wall.

B, is the second base plate, which is composed of some insulating material. Secured to the plate B, is a frame C, which carries an electric bell of the common type, and the gong c, which covers the electro-magnet D. The gong c, of the bell is insulated from the frame C, by the insulating piece c', but is in connection through the conducting piece el, with one pole of the battery. The transmitter is constructed with a metal concave speaking piece E of the ordinary type, which screws, as a cap, upon a back-'piece F, that is composed of any suitable insulating material. The diaphragm G is held in position between the cap E, and the back-piece F. The baclcpiece F, is provided with an axial screw f, by which it is secured to and contact made, with the frame C. The upper end or head of the screw f, consists of a disk g (see particularly Figs. 2 and 4) and between the disk g and the diaphragm G is placed the microphone h. The microphone consists of a disk composed of indiarubber or other suitable flexible insulating or non-conducting material, which is perforated so as to form cells when laid between two flat surfaces. The cells in the microphone 71. are filled with tine granulated carbon. The intimacy of contact between the particles of the granulated carbon in the cells and the contact surfaces between which the microphone is placed, is adjusted and regulated by the metal screw capF. of the transmitter. The

under surface of the diaphragm G, and the upper surface of the disk g, form the contact surfaces of the microphone and should be covered with plu mbago, graphite or other suitable form of carbon in order that the microphone shall be between two non-oxidizable surfaces. Metallic contact is made between the cap E, and the gong c, by means of a metal spring e, which is held between. the back-piece F, and the gong c. The frame C, is in contact with the earth. It will be seen by referring to Fig. 2that one pole of thebattery is in communication with the earth, through the conducting piece d, through the gong c through the contact piece e, through the cap E, the diaphragm G, the microphone h, the axial screw f, and bell frame C.

A flexible tube J, is secured to and hangs from the base plate A, and carries, at its free end the receiver which is of peculiar construction. The receiver comprises a dwarf'iron cylinder or shallow circular box K that is provided with a central adj ust-able projection lo, that forms a core of an electro-magnet L. The iron diaphragm M, of the receiver rests upon, and is in metallic contact with the edges of the shallow box K, and is retained in position, by means of a cap, which forms the earpiece N of the receiver. When a current passes through the electro-magnet L, the diaphragm M will form one pole of the magnet, and the free end of the core 7c, will form the other pole, thus rendering the diaphragm highly susceptible to the variations of current. One end of the wire of the electro-magnet L, forms contact with the shallow box Kwhile the other end of the wire terminates in a contact point in connection with a gravity switch O, see particularly Fig. 6. When the telephone is not in use, the receiver will hang pendent from the base plate A,as shown in Fig. 1 and the mercury o, in the gravity switch O, will close circuit with line and earth through the bell magnet Das shown in Fig. 6. But when the receiver is raised to the ear of the speaker, the mercury o, in the gravity switch will fall to the opposite end of its chamber, and circuit Will be closed from line to earth through the receiver, battery and transmitter. The iexible tube J,which is preferably composed of a helix of wire, serves as a conductorfrom the receiver magnet to the battery. Any other form of suitable gravity switch may be used, but the form of switch shown in the drawings is considered the best adapted for the purpose.

Fig. 8 is a diagram showing the circuits, when the instrument is at rest, and also when it is being used. When the instrument is at rest, the circuit is closed from the line, through the bell to earth; when the receiver is raised the gravity switch will close the circuit, from the line, through the receiver, through the battery, through transmitter, to earth. Each instrument may be provided with a battery.

Fig. 7 shows a modification of the above described arrangement of telephone, and is specially adapted for use at an office table or desk, so that the speaker may be in a position to use the telephone without leaving his seat. In ord er to meet the eXigencies of such a case, the transmitter is removed from the position it occupied in the arrangement first described, upon the gong, and is attached to one end of a rigid curved metal tube P the receiver being attached to ythe opposite end of the curved tube. The relative positions of the transmitter and the receiver, should be such, that, when the transmitter is placed opposite the mouth of the speaker, the receiver should naturally lie close to the ear of the speaker. When the instrument is not in use the transmitter should be hung upon a hook p, that is secured to the base plate A, the receiver remaining pendent, as in Fig. l.

In Fig. 2 the transmitter is in circuit, through the conducting piece d, andthe bell frame C, but in the arrangement shown in Fig. 7, conducting wires Q, are used, the wires being laid up in the form of a cord. Allowing for the slight modilication of the arrangement of conductors, the action of the apparatus is precisely similar to that previously described.

Having now particularly described and ascertained the nature ot' my said invention and in what manner the sameis to be performed, I declare that what I claim is:-

l. In telephones, a transmitter that is provided with a metal cup or mouth-piece the transmitter being superimposed upon a gong or call, in combination with a stem or screw by which the transmitter is secured to the framing that supports the gong or call, and with a contact piece (that is insulated from the stem or screw) and which makes contact with the metal cup or mouth piece of the transmitter, whereby a circuit is established through the metal cup, the diaphragm, the

microphone and the stem or screw as specitied.

2. In telephone transmitters a microphone consisting of granular or powdered conducting material such as granular carbon contained in cells or compartments formed in or by any suitable elastic non-conducting material such as india rubber the whole being placed between two non-oxidizable surfaces or electrodes and provided with an adjustable cap or cover for the purpose of regulating the normal degree of intimacy of contact between the granular material and the electrodes as herein described. A

3. In telephone transmitters, a microphone consisting of granular or powdered conducting material such as granular carbon, coniincd between two metallic contact plates coated with a film of carbon on their faces next to the granular carbon, to minimize oxidation of said metal contact plates substantially as described.

4. In telephones the combination of a receiver and transmitter with a flexible mechanical connection consisting of a helix of wire Awhich serves as a conductor from the receiver magnet to the battery, substantially as described.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

PARNELL RABBIDGE. Witnesses:

MANFIELD NEWTON, O'. E., DoNNELLY FISHER. 

